This invention relates generally to rock drills and more particularly to pneumatically operated percussive drills of the type adapted to be inserted into the drillhole being drilled thereby and commonly known as "down-the-hole" drills (DHD).
Many applications for down-the-hole drills require that fluids such as water and other matter be injected into the drill air supply to provide improved hole cleaning and stabilization. Typically, the volume of liquids injected can range from about 2.0 gallons per minute to about 15.0 gallons per minute. When water is injected into the air flow for a DHD, an appreciable loss in penetration rate results for a given pressure. The decrease in penetration rate can range from 30% to 60%, depending upon the fluid injection rate and pressure. The loss in hammer performance associated with fluid injection adversely affects DHD production and in many cases causes the use of DHD to be unsuitable.
The foregoing illustrates limitations known to exist in present down-the-hole drilling technology. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.